STONE. 345 
stances are given of fields being rendered barren 
by taking away the stones which covered them. 
Theophrastus accounts for this in a hot country, 
where it happened to the Corinthians, by saying, 
that the stones shelter the earth from the scorch- 
ing heat of the sun, and thereby preserve its 
moisture. The same holds true even in our 
colder latitudes, where the heat of the sun is less 
apt to hurt us; and Mr. Evelyn is clearly of 
opinion that husbandmen rather impoverish than 
improve those grounds which are almost covered 
with stones, especially where corn is sown, if they 
pick them off too minutely, because they thereby 
expose the land too much to the effects of heat 
and cold. Certain it is, that a moderate mix- 
ture of small gravel preserves the earth both 
warm and loose, and prevents too sudden ex- 
halations. But it seems highly probable that 
there must be some further reason, beyond what 
has yet been assigned, for the benefit arising from 
stones.” One ‘further reason’ is the assisting 
to keep open spongy and adhesive soils—and this 
has ceased to apply to the multitudes of once 
wet fields which have been improved and dried 
within the modern era of subsoil draining; and 
another and far more important ‘further rea- 
son’ is the composition of most of the kinds 
of stones,—and this both explains how the con- 
stant though slow disintegration of basalts, 
greenstones, clay porphyries, and especially cal- 
careous limestones by the combined action of 
tillage implements and the weather maintains 
fertility by supplying alkalies and salts for the 
nutrition of crops, and shows how the presence 
of sandstones, quartzose stones, and pieces of 
stubborn plutonic rocks either adds very little 
powdery matter of any description to the soil, 
or adds only such as contains scarcely any food 
for crops, and therefore does no appreciable good. 
Some stones, too, which have a widely different 
composition, or resolve themselves into widely 
different granules, from those of the mineral 
portion of the diluvium or alluvium in which 
they are imbedded, may do good by correcting 
the mechanical defects of the soil by their debris, 
or by contributing principles which chemically 
co-operate with those in the soil for producing 
recombinations of an alimentary nature to plants. 
Hence, any farmer who has a fair knowledge 
of the nature and functions of soils, and of the 
composition of all the most common kinds of 
rocks, may generally determine at a glance 
whether the stones in any field are beneficial ; 
and any farmer who has rot such a knowledge, 
and who wishes to determine whether the clean’ 
removal of stones in any case will do good or 
harm, ought by way of experiment to clear them 
away from one corner or small portion of the 
field, and observe the effects upon the next year 
or two’s cropping. 
The lifting and removal of large landfast boul- 
ders is a principal operation in the reclaiming of 
some waste lands, and has sometimes been found 
perplexing and very difficult. An excellent appa- 
ratus for lifting the stones is a tripod machine de- 
scribed upwards of twenty years ago, by Professor 
Low, in the Edinburgh Philosophical Journal and 
in the Transactions of the Highland Society. 
This consists simply of a set of sheerpoles, about 
14 feet in length,—a powerful tackle of pulleys 
suspended from the head of the poles,—an iron 
plug, comprising a ring, a flat part, and a cylin- 
der of about an inch in diameter and two inches 
in length hooked to the lower block of the tackle, 
—and a windlass six feet or more long, worked 
by levers, and having at each end a winch. It 
is placed over the stone to be raised by extend- 
ing the poles on three sides, and then the wind- 
lass is attached. If only a very small part of 
even a huge stone appear above the surface, it 
is enough; a circular hole must be drilled in it, 
with a mallet and the common steel-boring chisel 
of masons, about a sixteenth part of an inch less 
in diameter than the cylinder of the iron plug, 
and about two inches deep, and as nearly per- 
pendicular as possible ; the plug must be driven 
into the hole, to the depth of an inch or so, with 
a stroke or two of a hammer; and with no other 
fastening than this simple plug, the turning of 
the winches by as many persons as may be re- 
quisite will tear up the boulder, no matter though 
it should be of the utmost weight which a wag- 
gon can carry, through every opposing obstacle. 
The secure holding of the plug seems to result 
principally from the friction produced by the 
elasticity of the stone between the surfaces of the 
plug and the bore, and is so far exactly similar 
to the firm holding of a pin driven into a block 
of timber, with the difference that the elastic 
power of stone is incomparably greater than that 
of any timber; and perhaps it also arises partly 
from the circumstance that a line passing through 
the axis of the cylindrical plug will seldom if 
ever coincide with the vertical line passing 
through the stone’s centre of gravity when sus- 
pended by the plug, so that the plug’s resistance 
upon the sides of the bore is oblique, and occa- 
sions difficulty or impossibility of disengagement 
so long as the stone is in suspension. But when 
the stone is let down again, either ona cart or 
on the ground, the plug is loosened and let out 
simply by a smart stroke or two of a hammer 
near the edge of the bore. “ We shall often be 
surprised, in trying the experiment on large 
pieces of rock,” says Professor Low, “ to observe 
with how slight a seeming hold of the stone the 
masses will be torn up. Sometimes the iron pin 
is not driven above the fourth part of an inch 
into the stone before it becomes immoveable, 
and capable of raising a weight of many tons 
from the earth. When we consider the great- 
ness of the elastic power of the harder stones, 
as shown by this simple experiment, we may 
perhaps wonder that the ingenuity of man has 
not hitherto more applied so surprising a pro- 
perty to practical uses. It appears that, with a 
